I've admired the cockroach's ability to regrow lost legs since learning about them while working on my PhD in developmental genetics ages ago. Cut off a roach's appendage, and soon signals from the exposed cells stimulate division of neighboring cells at the injury site. And out grows a new leg.
The signaling pathways of both embryonic development and regeneration are common to many animal species, and are therefore ancient. The genes in control have intriguing names: Grainy Head, Notch, Wingless, Sonic Hedgehog, and even Hippo.
I remember reading about elegant experiments that moved the cells at the interface of an amputation in a model organism, such as the cockroach poster-child for regeneration. When a researcher rotated the cells at a cut site, a turned-around limb unfurled.
Salamanders can regenerate limbs too. Back in graduate school in Thom Kaufman's lab at Indiana University, we had two pet Mexican axolotls from the developmental biology group upstairs. Sally and Gerry Mander lived in a large rectangular tank above the vials of fruit flies, happily swimming, as amphibians do. And if a bit of a leg broke off from crashing into the side, the salamander could regrow it.
Of course humans can't regenerate missing limbs, or even toes. Our closest relatives that can are lizards (reptiles, not amphibians).
To continue reading, go to my DNA Science blog at Public Library of Science.